STP LOOP with WS-C3550-24-EMI

[wei.xiong]

I have two WS-C4507 with sup WS-X4515,two WS-C4507 is linked with etherchannal, one gbic of WS-C3550-24-EMI is linked to one and another gbic is linked to another WS-C4507.Now is often prompt:

01:23:51: %C4K_EBM-4-HOSTFLAPPING: Host 00:12:01:BE:16:3F in vlan 7 is flapping

between port Po1 and port Gi5/3

This is because of STP looped.

I have not configed STP because STP is enabled default on WS-C3550-24-EMI.

If I connected another WS-C3550-24-EMI,there is no above message.

thanks

[Kevin Dorrell]

I presume that one of the 4507 is the STP root, abd the other is the secondary root. if you go to the 3550 and do a show spanning-tree vlan 7, you should see one of the uplinks in forwarding, and the other in blocking. If not, there is something wrong that needs to be debugged urgently. Could you post the results of the command?

Do you have UDLD configured on the uplinks?

Make sure you do not have bpdu-filter set on the downlink ports on the 4507s - that will stop the STP working correctly on the 3550.

When you say you have tried with another 3550, do you mean in that same configuration, with the two uplinks?

Kevin Dorrell

Luxembourg

[wei.xiong]

Thank for your help

When I show span act,two uplink interfaces are in forwarding.I have not configed any thing about STP you mentioned.

If I try another 3550 without changing any configuration, it is ok.And the version of two 3550 is same.

The module in 4507 is ws-x4306.

Thanks

[Kevin Dorrell]

With the other 3550, I guess you see one link in forwarding and the other in blocking, don't you?

Just to check, is the root one of the 4507s?

This makes a difference to which switch we have to debug.

I am guessing we have a unidirectional link here.

Kevin Dorrell

Luxembourg